Process for the production of heterocyclic compounds

ABSTRACT

A process is provided for the continuous or semi-continuous production of hetero-macrocyclic compounds including lactones and cyclic esters. The process involves the catalyzed depolymerization of a linear polyester at an elevated temperature and under reduced pressure in the presence of a specified amount of monocarboxylate moieties and while providing top-to-bottom mixing throughout essentially the total volume of the reaction mass.

BACKGROUND OF THE INVENTION

Since the principle odor constituents of natural musks are macrocycliccompounds, numerous synthetic methods have been devised for thepreparation of various macrocycles in an attempt to duplicate thenatural musk odor. The method most commonly used for the preparation oflactones, ether-lactones and cyclic esters is the depolymerization ofthe corresponding linear polyester accompanied by ring closure. Forexample, lactones are obtained by depolymerizing the high molecularweight product obtained from the condensation of hydroxy acids, e.g.15-hydroxypentadecanoic acid. Similarly, macrocyclic esters result whenpolyesters obtained by the condensation of dicarboxylic acids and diolsare depolymerized.

Depolymerization procedures are described in U.S. Pat. No. 2,092,031,Czech Pat. No. 108,762 and the article by E. W. Spanagel and W. H.Carothers in J. Amer. Chem. Soc., Vol. 57, 929-934 (1935). In a typicalprocess of this type, the polyester is heated at an elevatedtemperature, but below the temperature of thermal decomposition, in thepresence of an inorganic catalyst. The catalyst is generally a chloride,nitrate, carbonate, borate, oxide, hydroxide or organic acid salt of adivalent metal such as magnesium, manganese, iron, cobalt, lead or tin.The depolymerization is carried out under reduced pressure and themacrocyclic compound and other volatile products formed during thecourse of the reaction removed from the reaction vessel.

While depolymerization procedures are presently considered to be thebest and therefore preferred method for synthesizing macrocycliclactones, ether-lactones and esters, such processes are not withoutcertain disadvantages. The principle difficulty with depolymerizationprocesses of this type is the viscosity of the reaction mass. The linearpolyesters are themselves highly viscous materials by virtue of theirhigh molecular weight but during the depolymerization reaction theviscosity is even further increased so that an intractable plastic massis formed due to chain-growth reactions occuring between partiallydepolymerized fragments present in the reaction mass. It is notuncommon, even during the very early stages of depolymerization, for thereaction mass to become so viscous that agitation by conventional meansis not possible. Heat transfer within such highly viscous, virtuallysolid reaction masses is very poor resulting in a highly inefficientreaction, namely, a slow rate of depolymerization and the formation oflarge amounts of undesirable by-products.

As a result of the viscosity/heat transfer problems associated withthese reactions, long reaction times are required even when using themost effective catalysts and reduced pressure and it is not feasible tocarry out these reactions on a large scale and obtain acceptable yieldsof the desired macrocyclic compounds. Accordingly, it has not heretoforebeen possible to carry out these depolymerizations as anything butbatch-type operations, thereby severely limiting the practical utilityof such processes for commercial purposes. Even with batch-typeoperations it has been necessary to conduct the reaction on a relativelysmall scale and unless very elaborate process equipment designed tomaximize heat transfer is used, it is possible to operate at only afraction of the total reactor capacity to avoid destructive thermaldecomposition, excessive foaming and other related problems. It would behighly advantageous therefore, if depolymerization processes could beconducted on a larger scale while minimizing the viscosity/heat transferproblems. It would be even more desirable if the depolymerization couldbe conducted as a continuous or semi-continuous operation and if highyields of the macrocyclic compounds were possible.

SUMMARY OF THE INVENTION

We have now quite unexpectedly discovered an improved process for theproduction of hetero-macrocyclic compounds, including lactones,ether-lactones, cyclic esters and cyclic ether-esters, by thedepolymerization of the corresponding linear polyesters. By this processit is possible to prepare macrocyclic compounds of good quality andminimize the formation of undesirable by-products. Also, this processovercomes many of the disadvantages associated with previously knownreactions resulting from poor heat transfer and the high viscosity ofthe reaction mass thereby making it possible to conduct this process ona larger scale than was heretofore possible if acceptable conversionswere to be obtained. Additionally, the process of this invention can beconducted as a continuous or semi-continuous operation.

To achieve the aforementioned improved results, the depolymerizationprocess of this invention is conducted at an elevated temperature andreduced pressure with a metal catalyst using agitation which providestop-to-bottom mixing throughout essentially the total volume of thereaction mixture and in the presence of at least 0.75 mole percent ofmonocarboxylate. The monocarboxylate moieties can be introduced into thesystem with the catalyst, with the polyester being depolymerized or bythe addition of a suitable ester to the reactor. The monocarboxylatemoieties can contain from about 6 to 40 carbon atoms but more preferablywill have 10 to 30 carbon atoms and will be present in the range 1.25 to5.0 mole percent. Top-to-bottom mixing throughout the reaction mass isachieved by the use of inverted multiple-blade conical vessels whereinthe blades have a helical configuration and are arranged to rotatethroughout essentially the entire reaction mass and in close proximityto the interior surface of the reactor and in a direction which providesdownward flow within the reaction mixture. Particularly advantageous arereactors formed by two inverted intersecting vertical cones and havingtwo conical helical ribbon blades which fit the inner contour of thebowl formed by the cones and whose axes coincide with the axes of thecones and which intermesh as they rotate in opposite directions at thesame speed.

Temperatures, pressures and catalysts used for the present improvedprocess can be varied. Reaction temperatures can range from 200° C. to400° C. but preferably will be between 250° C. and 350° C. The pressurewill typically be less than 50 mm Hg and more usually be between 0.1 mmHg and 10 mm Hg. From 0.1 to 10 weight percent of a metal oxide,hydroxide, halide or carboxylate of an organic acid is employed tocatalyze the depolymerization. While it is possible to employ compoundsof numerous metals for this purpose, magnesium, titanium, manganese,iron, cobalt, tin and lead compounds are preferred, particularly whenpresent in the range 0.1 to 5 weight percent.

DETAILED DESCRIPTION

The improved process of this invention is adaptable for the preparationof a wide variety of heterocyclic macrocyclic compounds. It isparticularly useful for the preparation of cyclic esters, cyclicether-esters, lactones and ether-lactones having 8 to 20 atoms in thering.

Hetero-macrocyclic compounds obtained by this process correspond to thegeneral formulae ##STR1## wherein R' is a bivalent hydrocarbon radical,which can be branched or straight chain, saturated or containunsaturation, having 1 to 15 carbon atoms, R₁ is a saturated bivalenthydrocarbon radical having 1 to 17 carbon atoms, R₂ is a saturatedbivalent hydrocarbon radical having 1 to 8 carbon atoms, A is a radicalselected from the group --O--, --S--, --NH-- and --NR*--, where R* is aC₁₋₄ alkyl group, and x is an integer from 0 to 4, and ##STR2## where R"is a bivalent hydrocarbon radical, branched or straight chain, saturatedor unsaturated having 1 to 18 carbon atoms, and R₁ and x are the same asdefined above and A is the same as defined above except that when x iszero A can only be oxygen.

The present improved process is especially useful for the production ofmacrocyclic esters corresponding to the formula ##STR3## wherein R₃ andR₄ are hydrogen or a C₁₋₄ alkyl group, R₅ is a saturated bivalenthydrocarbon radical having 2 to 13 carbon atoms, y is an integer from 0to 11 and A and x are the same as defined above. It is even moreadvantageous for the preparation of cyclic ester and ether-estercompounds of the general formula ##STR4## wherein R₆ and R₇ arehydrogen, methyl or ethyl groups, z is an integer from 1 to 4 and y isthe same as defined above. Especially preferred macrocyclic compoundsuseful as odorants in applications where fragrance chemicals are usedand corresponding to the formula ##STR5## where m is an integer from 4to 11 and n is 0 or 1 are prepared by the process of this invention andobtained in good yield and purity.

Illustrative macrocyclic esters and ether-esters which can be obtainedusing the depolymerization process of this invention include:tetradecamethylene carbonate, dodecamethylene oxalate,7-oxa-tridecamethylene oxalate, 3,6,9-tridecamethylene malonate,dodecamethylene malonate, decamethylene malonate, ethylene suberate,ethylene azelate, 3-oxa-pentamethylene azelate, 3-methylpentamethylenesebacate, ethylene undecanedioate, ethylene dodecanedioate, methylenedodecanedioate, methylene brassylate, ethylidine brassylate, ethylenebrassylate, ethylene-α-methylbrassylate,ethylene-α,α-dimethylbrassylate, ethylene-α-ethylbrassylate, and thelike. In addition to the aforementioned products still other productsincluding bicyclic and polycyclic materials such as hexamethylene cis(or trans)-tetra (or hexa) hydrophthalate can be obtained by the processof this invention.

More preferably the lactones obtained by the process of this inventionwill correspond to the formula ##STR6## wherein u is an integer from 5to 14, R₃, R₄, R₅ and x are the same as defined above and A is the sameas defined above except that when x is zero A can only be oxygen. Evenmore preferred lactones and ether-lactones of the formula ##STR7## wherev is 0, 1, or 2, R₅ and u are the same as defined above are obtained bythe present improved process. Exemplary lactones and ether-lactonescorresponding to the above formulae include: pentadecanolide,2-oxa-pentadecanolide, hexadecanolide, 3-oxahexadecanolide,10-oxahexadecanolide, 11-oxahexadecanolide, and 12-oxahexadecanolide.

To obtain the macrocyclic compound the corresponding linear polyester isdepolymerized in accordance with the procedure which will be describedmore fully below. For example, to obtain the cyclic ester correspondingto the formula (f) the polyester to be depolymerized will have repeatingunits of the formula ##STR8## where, R₆, R₇, y and z are the same asalready defined. The terminal groups of the polyester are not criticaland may be hydroxyl or hydrogen groups or, as will be more fullyexplained below, it may be advantageous to have the polyester cappedwith a monocarboxylic acid. Excellent results are obtained usingpolyesters which have a hydroxyl value. The preparation of the linearpolyester is not critical and plays no part in the present invention.The polyester is obtained using conventional condensation polymerizationtechniques known to the art. Generally, essentially equimolar amounts ofthe dicarboxylic acids and glycols, such as ethyleneglycol,diethyleneglycol or the like, are heated at an elevated temperature atreduced pressure for several hours. A catalyst may be employed which canbe particularly effective during the latter stages of thepolymerization. If desired, a monocarboxylic acid may be included toserve as a terminator. The linear polyesters, depending on theirmolecular weight and reactants from which they are formed, can rangefrom highly viscous liquids to solid waxy masses. Similarly to obtainlactones, polyesters obtained by the condensation of hydroxy-substitutedmonocarboxylic acids are employed. For the formation of ether-lactones,a polyester obtained by the condensation of a hydroxy acid containing anether linkage is depolymerized.

The above-described macrocyclic compounds are conveniently obtained inhigh yields and good purity from the improved process of this inventionwhich in general terms involves the catalyzed depolymerization of alinear polyester at an elevated temperature and under reduced pressurein the pressure of monocarboxylate moities and with agitation whichprovides top-to-bottom mixing throughout the total volume of thereaction mass. The temperature at which the depolymerization isconducted can be in the range of 200° C. to 400° C. but is necessarilybelow the thermal decomposition temperature of the polyester andmacrocyclic compound. More generally, the reaction temperature willrange from about 250° C. to about 350° C. In addition to the elevatedtemperature the depolymerization is conducted under reduced pressure,typically less than about 50 mm Hg and, more preferably, at a pressureless than about 10 mm Hg and to as low as 0.01 mm Hg. The temperatureand pressure employed will vary depending on the particular polyester tobe depolymerized and to a large extent will be governed by the design ofthe process equipment.

The depolymerization process is conducted in the presence of from about0.01 to 10% by weight, based on the polyester, of a metal catalyst.Numerous metal catalysts have been described in the prior art and can beused for the process of this invention. In general, Lewis acid metallicsalts of Group IIIa, IVa, IVb, Va, VIIb and VIII metals (Periodic Tableof the Elements, Handbook of Chemistry and Physics, 57th Ed., CRC press,Inc.) such as the oxides, hydroxides, halides or carboxylates of thesemetals are employed to catalyze the depolymerization. Especially helpfulin the process of this invention are the oxides, hydroxides, chloridesand carboxylates of organic acids having from 2 to 30 carbon atoms ofmagnesium, titanium, manganese, iron, cobalt, tin and lead. Lead and tincompounds are particularly advantageous. Products having low residualmetal contents are obtained using lead carboxylates of organic acidshaving from 8 to 22 carbon atoms. Best results are obtained when about0.1 to about 5 weight percent of the catalyst is used.

The catalyst may be present in the polyester or fed to the reactor assuch, in which case it may be charged at the outset of the reaction oradded continuously or incrementally during the course of thedepolymerization process. Since the catalyst can be combined with thepolyester prior to depolymerization, it is possible to employ the samemetal compound as catalyst for the preparation of the polyester and asthe polymerization catalyst, or if different catalysts are employed, thedepolymerization catalyst can be added to the polyester during the finalstage or at the end of the condensation reaction. Suitable catalysts forthe depolymerization process include but are not limited to lead (II)oxide, red lead, lead (II) oxalate, lead (II) stearate, lead (II)palmitate, lead (II) coconoates, cobalt (II) chloride, tin (II) oxide,tin (IV) oxide, tin (II) chloride, tin (II) oxalate, tin (II) stearate,iron (III) chloride, antimony (II) chloride, magnesium oxide, magnesiumchloride hexahydrate, manganese (II) chloride tetrahydrate, cobalt (II)chloride hexahydrate, iron (II) chloride tetrahydrate, n-butyl stannoicacid, di-n-butyl tin diacetate, condensed butyl titanate, and the like.

It has now quite unexpectedly been discovered that when thedepolymerization is conducted using the above-defined temperatures,pressures and catalysts and in the presence of a specified amount ofmonocarboxylate moieties and with agitation which provides top-to-bottommixing throughout essentially the total volume of the reaction mass,highly unexpected results are obtained. In accordance with the processof this invention it is possible to conduct the depolymerization as acontinuous or semi-continuous process while obtaining products of goodquality in high yield.

The monocarboxylate ##STR9## moieties can result from any one of severalsources or a combination thereof, so long as the concentration of themonocarboxylate is at least 0.75 mole percent. The source of themonocarboxylate may be the catalyst, such as when a metalmonocarboxylate catalyst is employed, or they can be introduced into thereaction system as the terminating group of the polyester to bedepolymerized, such as when the polyester is capped with amonocarboxylic acid. Also, monocarboxylate may be introduced into thesystem by the addition of a suitable ester, such as ethylene distearate,during the depolymerization. The concentration of the monocarboxylatemoieties can range as high as 10 mole percent and in some cases evenhigher, however, practical and economic considerations dictate that themonocarboxylate concentration be kept as low as possible. Preferably themonocarboxylate will range between 1.25-5.0 mole percent. If theconcentration of monocarboxylate is too high excessive amounts of solidresidues will be formed. Also, the possibility that esters of thesemonocarboxylates will be carried over with the macrocyclic compoundsduring the distillation is increased thereby making purification of theresulting macrocyclic compound more difficult. The monocarboxylatemoieties are derived from monocarboxylic acids, aliphatic or aromatic,which can contain from about 6 to 40 carbon atoms and, more preferably10 to 30 carbon atoms. Excellent results are obtained using a mixture ofaliphatic monocarboxylates having varying chain lengths of typicallybetween about 10 and 30 carbon atoms.

In addition to the presence of carboxylate moieties within theabove-defined limits, the present improved process is necessarilyconducted with agitation which provides top-to-bottom mixing throughoutessentially the total volume of the reaction mass. This type ofagitation, in addition to providing effective heat transfer throughoutthe entire reaction mixture, also serves to reduce foaming within thereactor and provides a means for conveniently discharging the solidhighly crosslinked residues formed during the depolymerization as aresult of chain-growth reactions occurring between partiallydepolymerized and thermally decomposed polymer fragments from thereaction without completely shutting down the reactor. By essentiallytotal volume mixing is meant that there are no "hot spots" within thereaction mixture so that highly efficient heat transfer within thereaction mass which contains solid polymeric residue dispersed thereinis obtained and undesirable thermal degradation is minimized.

The specific equipment employed for the conduct of this process can varyand, in general, any means capable of achieving the prescribed mixingcan be employed. A particularly useful means of agitation which providestop-to-bottom mixing and a highly efficient dividing-recombining actionthroughout essentially the entire volume of the mass are invertedmultiple-blade conical vessels wherein the blades have a helical ribbonconfiguration and are arranged to rotate throughout essentially theentire mass and in close proximity to the interior surface of the bowland in the direction which provides a downward flow within the reactionmass. Such equipment is known to the art and typical mixers and reactorsof this type are described in U.S. Pat. Nos. 3,226,097, 3,314,660, and3,352,543. The blades can be on a single shaft or mounted on separateshafts and they can be rotated in different directions and/or atdifferent speeds and the pitch varied. When the blades are on a singleshaft, the outer blade will trace an envelope essentially conforming tothe interior shape of the reactor bowl while the interior helicalblade(s) trace an envelope from and within the outer envelope andthroughout the remainder of the reaction mass.

Reactors having two conical, helical ribbon blades which fit the innercontour of the bowl formed by two inverted intersecting vertical conesand whose axes coincide with the cone axes of the bowls and whichintermesh as they rotate at the same speed in opposite directions areparticularly useful for the conduct of the present improveddepolymerization process and form a preferred embodiment thereof. Withthis type of equipment it is possible to adjust the blade-to-blade andblade-to-wall clearance by retracting each blade along its axis so thathighly efficient mixing is obtained within the viscous plastic massthereby obtaining maximum heat transfer which optimizes depolymerizationof the polyester and minimizes the formation of undesirable by-productsresulting from thermal degradation. The blades can rotate at up to 200rpm but usually will be operated at a speed of 5 to 60 rpm.

It has been found that the rate of depolymerization obtained by theprocess of this invention is considerably faster than obtainedwithheretofore known batch-type operations and higher yields arepossible. Mixing of the reaction mass and the corresponding improvementof the heat transfer characteristics of the reaction mass are possibleonly by using the above-defined agitation in the presence of thespecified amount of monocarboxylate. When the monocarboxylate moietiesare not present or are below the minimum concentration required, theagitation is ineffective and a solid mass is formed within the reactionwhich is impossible to agitate or if agitation does continue the mass"climbs up" the agitator so that efficient heat transfer is notpossible.

Macrocyclic compounds obtained by the present process are primarilyuseful in applications where fragrance materials are employed. Forexample, the products of this process have utility in detergents (heavyduty and regular laundry), soaps (bar soaps, dish soaps and specialtybeauty soaps), personal care products (bath oils, shampoos, hair rinses,deodorants, shaving creams) and as fine fragrance components forperfumes, perfume oils, perfume fixatives, colognes aftershave lotionsand the like.

The following examples illustrate the invention more fully but are notintended to limit the scope thereof. In these examples, all parts andpercentages are on a weight basis unless otherwise indicated.

EXAMPLE I

Poly(ethylene brassylate) was prepared by charging to a top-agitatedresin kettle fitted with a distillation head and condenser 109 partsdimethyl brassylate containing approximately 2.3 mole percent methylesters of monocarboxylic acids and 30.5 parts polymer grade ethyleneglycol. A supported titanium catalyst (0.08 part), prepared fromtetraisopropyl titanate and a naturally acidic montmorillonite clay inaccordance with the teachings of U.S. Pat. No. 4,032,550, was added tothe reaction mixture under a positive pressure of nitrogen and heatingbegun. When the temperature of the reaction mixture reached about 180°C. methanol began distilling from the reaction mixture and wascollected. After most of the methanol was removed and the temperatureincreased to about 195° C.-205° C., a vacuum of 2 in. Hg was applied andincreased slowly to 30 in. Hg. Samples were periodically removed fromthe reaction mixture for analysis and after about 11 hours the reactionmixture had an acid value of 0.1 and hydroxyl value of 15.3. Heating wasterminated at this point, the reaction mixture cooled to about 180° C.and the vacuum with nitrogen. The high molecular weight poly(ethylenebrassylate), viscosity of 177 centistokes at 210° C., was filtered toremove the supported titanium catalyst.

After dissolving 1.36 weight percent lead stearate into theabove-prepared product, it was transferred to a stainless steel tank andmaintained at 120° C. with agitation. From this tank the product wasmetered into an electrically heated two gallon stainless steel invertedvertical cone reactor fitted with two conical, helicoidal blades whoseaxes coincide with the cone axes of the bowl and which intermesh as theyrotate in opposite directions to provide top-to-bottom mixing throughoutthe total volume of the reaction mixture. The blades are positionedwithin the reactor so that the maximum blade-to-wall clearance (distancebetween the blades and the interior surface of the reactor) is about0.25" and the blades are driven with a high torque motor at about 20rpm. A vacuum of about 1-2 mm Hg is maintained throughout the reaction.The rate of addition of poly(ethylene brassylate) was approximately fourpounds per hour for the first two hours after which time the rate wasadjusted to 1.5 pounds per hour and the addition continued for another41/2 hours. Ethylene brassylate was continuously distilled from thereactor and collected. The rate of ethylene brassylate recovery wasessentially constant after about 11/2 hours and was maintained for about12 hours after which time it slowly decreased as the amount ofpoly(ethylene brassylate) in the reactor was depleted. After about 18hours (total reaction time), at which time ethylene brassylate was beingcollected at a rate of only 0.25 pound per hour or less, the reactiontemperature was reduced, the vacuum broke with nitrogen and the valve atthe bottom of the reaction opened to discharge of the solid residuepresent in the reactor. The brownish granular material, believed to becrosslinked polyester, was extruded through the orifice by the action ofthe blades. When no further material could be extruded the port wasclosed, the temperature and pressure adjusted to within the operatingrange and the charging and entire cycle repeated in the manner describedabove. The depolymerization reaction was repeated in thissemi-continuous manner through three complete cycles withoutencountering processing difficulties and without significantly affectingthe rate of reaction or conversion. Conversions ranged from about 70 to80% based on the weight of the poly (ethylene brassylate).

EXAMPLE II

In a manner similar to that described for Example I, 75 parts dimethylbrassylate and 38 parts ethylene glycol were reacted in the presence of0.1 part stannous oxalate. The reaction mixture was heated for about51/2 hours at 160 to 185° C. under a nitrogen atmosphere with methanoldistilling from the reaction mixture. A vacuum was applied and thereaction continued with the concurrent distillation of ethylene glycolfor an additional 31/2 hours. Additional stannous oxalate (0.4 part) wasadded with 0.82 part ethylene glycol distearate and the reactioncontinued for 6 hours at a temperature of about 185°-210° C. andpressure of 1 in. Hg. At the completion of the reaction period the tincontent was increased by the addition of additional stannous oxalate. Anamount of ethylene glycol distearate about comparable to the initialamount charged was also added and the mixture agitated at 185° C. undernitrogen for about one hour. The resulting polyester product containing0.3 mole percent tin catalyst was depolymerized following thesemi-continuous procedure already described and operating on twenty-fourhour cycles. The temperature was maintained at about 290° C.-300° C. at0.3 and 0.6 mm Hg while agitating the reaction mass at a rate of 20-30rpm. The average feed rate was about 2.2 pounds/hour and the averagerate of recovery of ethylene brassylate was 0.89 pound/hour with amaximum rate of 1.72 lbs/hour. At the end of the cycle period thegranular powder was extruded from the reactor, vacuum reapplied to thesystem while increasing the temperature to within the operating rangeand the process continued.

When the equipment is modified to permit the solid product formed duringthe depolymerization to be removed without disrupting the operatingconditions within the reactor, the depolymerization can be carried outas a continuous operation. This is accomplished by attaching a suitablecollection and discharging means to the bottom of the reactor so that asthe granular product begins to build up within the reactor it can beisolated from the principal reaction zone without disrupting theoperating conditions therein and removed. The solid material which isremoved can be discarded or it can be fed from the primary reactor intoanother reactor or reaction zone where it is possible, as a result ofdesign variations and/or different operating conditions, to further"cook down" the crosslinked polyester and thereby obtain still higherconversions of the poly(ethylene brassylate).

EXAMPLE III

Diethyleneglycol azelate was obtained by the depolymerization ofpoly(diethyleneglycol azelate) obtained by condensing diethylene glycoland azelaic acid using stannous stearate as the catalyst. The mole ratioof the respective reactants and catalyst was 1.0:0.67:0.027. Thecatalyst was added after about 7 hours reaction when the rate of waterevolution slowed. The maximum pot temperature was about 200° C. andafter addition of the catalyst the pressure was reduced to 0.6 mm Hg.The resulting polyester containing 0.64 weight percent Sn wasdepolymerized in much the same manner as described in Example I, thatis, by continuously charging the polyester to the heated (270°-310° C.),agitated (30-40 rpm) reactor under reduced pressure (0.2-0.8 mm Hg) overa period of about nine hours while continuously removingdiethyleneglycol azelate until the recovery rate dropped to anunacceptable level, i.e. significantly below the maximum recovery rateof 3.5 pounds per hour. At this point the solid crosslinked polymericmaterial formed in the reactor was discharged and the process repeated.The yield of diethyleneglycol azelate obtained during the firstdepolymerization cycle was 86.7%.

EXAMPLE IV

Ethylene dodecanedioate was prepared by the depolymerization ofpoly(ethylene dodecanedioate) containing 1.36 weight percent leadstearate and 1.8 mole percent ethylene distearate so that the totalmonocarboxylate concentration in the polyester was 3.5 mole percent. Thereaction was conducted at a maximum temperature of 320° C. with apressure of about 0.3-0.4 mm Hg while agitating the reaction mass at 20rpm. The rate of recovery of ethylene dodecanedioate ranged from about0.88 to 1.1 pounds per hour and the conversion of poly(ethylenedodecanedioate) to be the desired product was 53%.

EXAMPLE V

Pentadecanolide was prepared by depolymerizing a mixed polyestercomprised predominantly of 15-hydroxypentadecanoic acid containing minoramounts of dibasic acids and some mono- and difunctional alcohols. Thereaction mixture was agitated at 20 rpm and the reaction temperaturemaintained between about 295° C. and 320° C. at a pressure between 0.25and 0.9 mm Hg. A conversion of 58% was obtained and the maximum rate ofrecovery of pentadecanolide was 1.0 pounds per hour. The cycle time forthe depolymerization was about 18 hours and no difficulties wereencountered during subsequent cycles.

We claim:
 1. In a process for the production of hetero-macrocycliccompounds selected from the group consisting of cyclic esters andlactones having 8 to 20 carbon atoms in the ring by depolymerization ofa linear polyester and ring closure at an elevated temperature andreduced pressure and in the presence of a metal catalyst, theimprovement comprising conducting the process as a continuous orsemi-continuous operation in the presence of 0.75 to 10 mole percentmonocarboxylate derived from an aliphatic monocarboxylic acid having 6to 40 carbon atoms and with agitation which provides top-to-bottommixing throughout essentially the total volume of the reaction mass inan inverted multiple-blade conical vessel wherein the blades have ahelical configuration and are arranged to rotate throughout essentiallythe entire reaction mass and in close proximity to the interior surfaceof said conical vessel and in a direction which provides a downward flowwithin the reaction mixture.
 2. The process of claim 1 wherein themonocarboxylate is present at a concentration of 1.25 to 5.0 molepercent .
 3. The process of claim 2 wherein said conical vessel isformed by two inverted intersecting vertical cones fitted with twoconical helical ribbon blades, which fit the inner contour of the bowlformed by the cones and whose axes coincide with the axes of the cones,and which intermesh as they rotate in opposite directions at the samespeed.
 4. The process of claim 1 wherein the reaction temperature isbetween 200° C. and 400° C., the pressure is less than 50 mm Hg, fromabout 0.01 to 10 weight percent of an oxide, hydroxide, halide orcarboxylate of an organic acid having from 2 to 30 carbon atoms of aGroup IIIa, IVa, IVb, Va, VIIb or VIII metal is employed to catalyze thedepolymerization and the hetero-macrocyclic compound is a cyclic esteror cyclic ether-ester corresponding to the formula. ##STR10## wherein R'is a bivalent hydrocarbon radical having 1 to 15 carbon atoms, R₁ is asaturated bivalent hydrocarbon radical having 1 to 17 carbon atoms, R₂is a saturated bivalent hydrocarbon radical having 1 to 8 carbon atoms,A is oxygen or sulfur, and x is an integer from 0 to 4, or a lactone orether-lactone corresponding to the formula ##STR11## wherein R₁ and xare the same as defined above, R" is a bivalent hydrocarbon radicalhaving 1 to 18 carbon atoms and A is the same as defined above exceptthat when x is zero A can only be oxygen.
 5. The process of claim 4wherein the catalyst is an oxide, hydroxide, chloride or carboxylate ofa metal selected from the group consisting of magnesium, titanium,manganese, iron, cobalt, tin and lead and the cyclic ester or cyclicether-ester corresponds to formula (c) wherein R' is the bivalenthydrocarbon radical --CR₃ R₄ --CH₂)_(y) wherein R₃ and R₄ are hydrogenor a C₁₋₄ alkyl group and y is an integer from 0 to 11, R₁ and R₂ aresaturated bivalent hydrocarbon radicals having 2 to 13 carbon atoms andA and x are the same as defined above and the lactone or ether-lactonecorresponds to formula (d) wherein R" is the bivalent hydrocarbonradical --CH₂)_(u) CR₃ R₄ -- where u is an integer from 5 to 14, R₁, R₃,R₄ and x are the same as previously defined and A is the same as definedabove except that when x is zero A can only be oxygen.
 6. The process ofclaim 5 wherein the reaction temperature is between about 250° C. and350° C., the pressure is in the range 0.01 to 10 mm Hg, about 0.1 toabout 5 weight percent of the catalyst is used and the concentration ofmonocarboxylate ranges between 1.25 and 5 mole percent.
 7. The processof claim 6 wherein the depolymerization is carried out in a conicalvessel formed by two inverted intersecting vertical cones fitted withtwo conical helical ribbon blades, which fit the inner contour of thebowl formed by the cones and whose axes coincide with the axes of thecones, and which intermesh as they rotate in opposite directions at thesame speed.
 8. The process of claim 7 wherein the catalyst is an oxide,hydroxide, chloride or carboxylate of lead or tin.
 9. In a process forthe production of a lactone or ether-lactone having 8 to 20 carbon atomsin the ring and corresponding to the formula ##STR12## wherein R₅ is asaturated bivalent hydrocarbon radical having 2 to 13 carbon atoms, u isan integer from 5 to 14 and v is zero, 1 or 2 by depolymerization of alinear polyester and ring closure at a temperature between about 250° C.and 350° C., pressure in the range 0.01 to 10 mm Hg and in the presenceof about 0.1 to 5 weight percent of an oxide, hydroxide, chloride orcarboxylate of a metal selected from the group consisting of magnesium,titanium, manganese, iron, cobalt, tin and lead, the improvementcomprising conducting the process as a continous or semi-continuousoperation in the presence of 1.25 to 5 mole percent monocarboxylatederived from an aliphatic monocarboxylic acid having 6 to 40 carbonatoms and with agitation which provides top-to-bottom mixing throughoutessentially the total volume of the reaction mass in an invertedmultiple-blade conical vessel wherein the blades have a helicalconfiguration and are arranged to rotate through essentially the entirereaction mass and in close proximity of the interior surface of saidconical vessel and in a direction which provides a downward flow withinthe reaction mixture.
 10. In a process for the production of a cyclicester or cyclic ether-ester having 8 to 20 carbon atoms in the ring andcorresponding to the formula ##STR13## wherein R₆ and R₇ are hydrogen,methyl or ethyl groups, y is an integer from 0 to 11 and z is an integerfrom 1 to 4 by depolymerization of a linear polyester and ring closureat a temperature between about 250° C. and 350° C., pressure in therange 0.01 to 10 mm Hg and in the presence of about 0.1 to 5 weightpercent of an oxide, hydroxide, chloride or carboxylate of a metalselected from the group consisting of magnesium, titanium, manganese,iron, cobalt, tin and lead, the improvement comprising conducting theprocess as a continuous or semi-continuous operation in the presence of1.25 to 5 mole percent monocarboxylate derived from an aliphaticmonocarboxylic acid having 6 to 40 carbon atoms and with agitation whichprovides top-to-bottom mixing throughout essentially the total volume ofthe reaction mass in an inverted multiple-blade conical vessel whereinthe blades have a helical configuration and are arranged to rotatethrough essentially the entire reaction mass and in close proximity ofthe interior surface of said conical vessel and in a direction whichprovides a downward flow within the reaction mixture
 11. In a processfor the production of a cyclic ester of cyclic ether-ester having 8 to20 carbon atoms in the ring and corresponding to the formula ##STR14##wherein m is an integer from 4 to 11 and n is 0 or 1 by depolymerizationof a linear polyester and ring closure at a temperature between about250° C. and 350° C. pressure in the range 0.01 to 10 mm Hg and in thepresence of about 0.1 to 5 weight percent of an oxide, hydroxide,chloride or carboxylate of lead or tin, the improvement comprisingconducting the process as a continuous or semi-continuous operation inthe presence of 1.25 to 5 mole percent monocarboxylate derived from analiphatic monocarboxylic acid having 6 to 40 carbon atoms and withagitation which provides top-to-bottom mixing throughout essentially thetotal volume of the reaction mass in a conical vessel formed by twoinverted intersecting vertical cones fitted with two conical helicalribbon blades which fit the inner contour of the bowl formed by thecones and whose axes coincide with the axes of the cones and whichintermesh as they rotate in opposite directions at the same speed so asto provide downward flow within the reaction mixture.
 12. The process ofclaim 11 wherein the catalyst is a lead carboxylate of an organic acidhaving from 8 to 22 carbon atoms.
 13. The process of claim 12 whereinthe hetero-macrocyclic compound is ethylene brassylate.